There is plenty water in the oceans, but I've read that deep in the crust/mantle of the earth within crystals and other rockforms is water enclosed. So could it be possible that there is more water beneath the surface of the earth than above?
Clearly you are referring to water locked up in hydrous minerals. The short answer is no, not much water in the Earth at all compared to the surface. The hotter it gets the more hydrous minerals tend to dehydrate, so there are only minuscule traces of water at great depth. I suggest you calculate a rough water balance of water carried into subduction zones = length of subduction zone x thickness x sediment porosity (under pressure) x average subduction rate. This should be compared with estimates of volcanic emission of water vapour (both to the atmosphere and submarine - more difficult to estimate). I'm guessing these should be more or less in equilibrium. The water volume involved is trivial compared to the water on the oceans.